GaN SUBSTRATE, EPITAXIAL LAYER-PROVIDED SUBSTRATE, METHODS OF MANUFACTURING THE SAME, AND METHOD OF MANUFACTURING SEMICONDUCTOR DEVICE

ABSTRACT

A GaN substrate on which an epitaxially grown layer of good quality can be formed is obtained. A GaN substrate as a group III nitride substrate has a surface in which the number of chlorine atoms per square centimeter of the surface is not more than 2×10 14 , and the number of silicon atoms per square centimeter of the surface is not more than 3×10 13 , wherein a plane orientation of the surface is any of a (0001) plane, a (11-20) plane, a (10-12) plane, a (10-10) plane, a (20-21) plane, a (10-11) plane, a (11-21) plane, a (11-22) plane, and a (11-24) plane of a wurtzite structure.

TECHNICAL FIELD

The present invention relates to a group III nitride substrate, anepitaxial layer-provided substrate, methods of manufacturing the same,and a method of manufacturing a semiconductor device. More particularly,the present invention relates to a GaN substrate as an example of agroup III nitride substrate on which an epitaxial layer of good filmquality can be formed, an epitaxial layer-provided substrate, methods ofmanufacturing the same, and a method of manufacturing a semiconductordevice.

BACKGROUND ART

Conventionally, compound semiconductor substrates including a group IIInitride substrate such as a GaN substrate, having a mirror polishedsurface on which an epitaxially grown layer is formed by epitaxy, havebeen utilized in various semiconductor devices such as a light emittingdevice, a power device, and the like. There has been a problem that, ifa haze occurs on a surface mirror polished as described above, a defectsuch as unevenness occurs in an epitaxially grown layer formed thereon,causing deterioration in the quality of the epitaxially grown layer.Therefore, various polishing methods suppressing occurrence of a haze(i.e., reducing a haze level) as described above have conventionallybeen proposed (for example, as to GaAs, see Patent Document 1 (JapanesePatent Laying-Open No. 11-347920)).

-   Patent Document 1: Japanese Patent Laying-Open No. 11-347920

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, it has been found as a result of the inventors' examinationthat a mere reduction in the haze level of a surface of a group IIInitride substrate such as GaN may cause a defect such as unevenness inan epitaxially grown layer formed on the surface. In this case, it hasbeen difficult to sufficiently reduce the probability of occurrence of adefect in an epitaxially grown layer even by applying a conventionalpolishing method described above.

The present invention has been made to solve the aforementionedproblems, and one object of the present invention is to provide a groupIII nitride substrate on which an epitaxially grown layer of goodquality can be formed, and a method of manufacturing the same.

Another object of the present invention is to provide an epitaxiallayer-provided substrate including an epitaxially grown layer of goodquality and a method of manufacturing the same, and a method ofmanufacturing a semiconductor device using the epitaxial layer-providedsubstrate, utilizing a group III nitride substrate as described above.

Means for Solving the Problems

The inventors have studied the mechanism that causes quality degradationin an epitaxially grown layer formed on a surface of a group III nitridesubstrate. Specifically, the inventors have performed detailedinspections (such as measurement of the types and number of adheringmaterials) on a surface of a group III nitride substrate prior to theformation of an epitaxially grown layer thereon, and studied thecorrelation between the inspection result and the quality of the formedepitaxially grown layer. As a result, the inventors have found that thenumber of atoms of an acid material and the number of silicon atomspresent on a surface of a group III nitride substrate at the time offorming an epitaxially grown layer have a significant influence on thequality of the formed epitaxially grown layer. Herein, the group IIInitride substrate refers, for example, to a substrate made of GaN, asubstrate made of MN, and a mixed crystal substrate thereof(Ga_(x)Al_(y)N). Further, the acid material refers to a material thatexhibits acidity when it reacts with water or is dissolved in water,including halogen such as chlorine, fluorine, bromine, iodine, and thelike, nitrogen oxide (NO_(x)), sulfur oxide (SO_(x)), hydrogen chloride,and the like.

The inventors have examined the reason that the acid material describedabove adheres to the surface of the group III nitride substrate, andpresumed occurrence of a phenomenon as described below. Specifically, ina step of manufacturing a group III nitride substrate (for example, aGaN substrate), volatile acid materials such as hydrochloric acid andnitric acid are used, and in addition, a polishing solution containingabrasive grains is used to polish the substrate. A chlorine-basedoxidizing agent is often used in the polishing solution, and a largeamount of chlorine, which is an acid material, is contained in thepolishing solution. A polishing step using these acid materials isgenerally performed with an atmosphere within a polishing apparatusemitted by an emission apparatus. If the emission apparatus cannot emitall the acid material, a portion of the acid material is present in theatmosphere within the polishing apparatus. It is considered that, inthis case, the acid material is adsorbed on the surface of the group IIInitride substrate. It is also considered that such an acid materialreacts with an element constituting the group III nitride substrate toform a deposit on the substrate surface. If such a deposit is formed,values of the surface roughness and the haze level of the substratesurface are increased.

After being polished, the group III nitride substrate is cleaned, andthen subjected to a surface inspection. If the acid material is presentin large amount on the surface of the group III nitride substrate in thepolishing step described above, it is difficult to remove the acidmaterial sufficiently in a later step. Therefore, values of the surfaceroughness and the haze level of the substrate surface in a final stateare increased. Further, the surface inspection is performed within aclean room, and the group III nitride substrate is exposed to anatmosphere within the clean room during the inspection, for at leastabout one hour. It is also considered that, on this occasion, a minuteamount of the acid material flowing from the polishing step describedabove or the like is adsorbed on the surface of the group III nitridesubstrate.

Further, when a group III nitride substrate such as a GaN substrate ispolished using a polishing solution containing a material containing Siatoms such as SiO₂ as abrasive grains, the Si containing material may beleft on the substrate surface even though a cleaning step is performedafter polishing. The inventors have found that, if the acid material(and/or the deposit) and the Si containing material described above arepresent to an excessive degree on the surface of the group III nitridesubstrate, the quality of an epitaxially grown layer formed on thesubstrate surface is deteriorated. That is, in order to form ahigh-quality epitaxially grown layer on the surface of the group IIInitride substrate, it is effective to reduce concentrations of the acidmaterial and the Si containing material described above on the substratesurface. The inventors have then found that, in order to reduce theconcentration of the acid material on the substrate surface as describedabove, it is effective to reduce the concentration of the acid materialin an ambient gas in contact with the substrate surface within apolishing apparatus, as much as possible. Further, the inventors havefound that, in order to reduce the concentration of the Si containingmaterial (or silicon atoms) adhering to the substrate surface, it iseffective that a polishing solution used in the polishing step containsan acid and a surface-active agent. It is to be noted that the problemthat the concentration of the acid material on the substrate surface isincreased when the concentration of the acid material within anatmosphere in the manufacturing step is high occurs not only in thepolishing step and the inspection step, but also in other steps.

A group III nitride substrate according to the present invention made bythe findings described above has a surface in which a number of atoms ofan acid material per square centimeter of the surface is not more than2×10¹⁴, and a number of silicon (Si) atoms per square centimeter of thesurface is not more than 3×10¹³, wherein a plane orientation of thesurface is any of a (0001) plane, a (11-20) plane, a (10-12) plane, a(10-10) plane, a (20-21) plane, a (10-11) plane, a (11-21) plane, a(11-22) plane, and a (11-24) plane of a wurtzite structure, and thegroup III nitride substrate is made of a group III nitride. Further, thegroup III nitride substrate is preferably a GaN substrate, and the atomsof the acid material are preferably chlorine atoms. It is to be notedthat the description that a plane orientation of the surface of thesubstrate is “any of a (0001) plane, a (11-20) plane, a (10-12) plane, a(10-10) plane, a (20-21) plane, a (10-11) plane, a (11-21) plane, a(11-22) plane, and a (11-24) plane of a wurtzite structure” refers to acase where the plane orientation of the substrate is completelyconsistent with each plane orientation described above, as well as acase where an off angle from each plane orientation listed as describedabove is not more than 15°. In addition, the off angle is preferably notmore than 10°, and more preferably not more than 5°.

With this construction, an epitaxially grown layer of good quality canbe formed on the surface of the group III nitride substrate. It is to benoted that the reason for setting the number of atoms of the acidmaterial per square centimeter of the surface of the group III nitridesubstrate to not more than 2×10¹⁴ is that, if the number of atoms of theacid material is suppressed to not more than this degree, the roughnessand the haze level of the substrate surface can be reduced sufficiently(i.e., the degree of unevenness of the substrate surface can be reducedsufficiently). Further, the reason for setting the number of silicon(Si) atoms per square centimeter of the surface to not more than 3×10¹³is that, with this setting, the quality of the formed epitaxially grownlayer (for example, the surface roughness and the film quality of theepitaxially grown layer) can be maintained sufficiently good (forexample, a prescribed light emission intensity can be obtained when theepitaxially grown layer is utilized as a light emission layer of a lightemitting device). It is to be noted that, if the acid material ispresent as a simple substance such as halogen including fluorine,chlorine, bromine, iodine, and the like, the number of atoms of the acidmaterial refers to the number of halogen atoms, and if the acid materialis present as a compound such as nitrogen oxide (NO_(x)), sulfur oxide(SO_(x)), or the like, the number of atoms of the acid material refersto the number of molecules of the compound. Further, if silicon ispresent as a simple substance, the number of silicon atoms refers to thenumber of atoms of the silicon, and if silicon is present as a compoundsuch as SiO₂, the number of silicon atoms refers to the number ofmolecules of the compound.

In the group III nitride substrate described above, the haze level ofthe surface may be not more than 5 ppm. This is because the surfaceroughness of the group III nitride substrate can be reduced sufficientlyby setting the number of atoms of the acid material (the density of theacid material) per square centimeter of the surface of the substrate tonot more than the value as described above, and thus the degree of haze(haze level) can also be reduced sufficiently. By reducing the hazelevel of the substrate surface as described above, quality deteriorationof the epitaxially grown layer formed on the substrate surface can beprevented. It is to be noted that the reason for setting the upper limitof the haze level to 5 ppm is that, if the haze level is more than 5ppm, the quality of the formed epitaxially grown layer is deteriorated,and sufficient light emission intensity cannot be obtained when theepitaxially grown layer is utilized for example as a light emissionlayer of a light emitting device.

In a group III nitride substrate according to the present invention, anumber of silicon atoms per square centimeter of a surface is not morethan 3×10¹³, and a haze level of the surface is not more than 5 ppm.Further, in a group III nitride substrate according to the presentinvention, a number of atoms of an acid material per square centimeterof a surface is not more than 2×10¹⁴, and a haze level of the surface isnot more than 5 ppm.

With this construction, an epitaxially grown layer of good quality canbe formed on the surface of the group III nitride substrate.

In the group III nitride substrate described above, the number of atomsof the acid material per square centimeter of the surface is preferablynot more than 9×10¹³. Further, in the group III nitride substratedescribed above, the haze level of the surface is preferably not morethan 3 ppm. Furthermore, in the group III nitride substrate describedabove, the number of silicon atoms per square centimeter of the surfaceis preferably not more than 1×10¹³.

In this case, the film quality of the epitaxially grown layer formed onthe surface of the group III nitride substrate can be further improved.For example, when the substrate is used to form a light emitting deviceand the epitaxially grown layer is used to form a light emission layer,light emission intensity of the light emission layer can be furtherincreased.

An epitaxial layer-provided substrate according to the present inventionincludes a base substrate made of a group III nitride, and anepitaxially grown layer formed on a surface of the base substrate. Anumber of silicon (Si) atoms per cubic centimeter at an interfacebetween the base substrate and the epitaxially grown layer is not morethan 1×10²⁰.

In the epitaxial layer-provided substrate constructed as describedabove, the epitaxially grown layer is formed with the number of siliconatoms on the surface of the base substrate maintained low, and thus theepitaxially grown layer can be formed to have good film quality.Therefore, occurrence of a problem that, when the epitaxiallayer-provided substrate described above is used to form a semiconductordevice (for example, a light emitting device), the semiconductor devicedoes not offer sufficient performance (i.e., becomes defective) due topoor quality of the epitaxially grown layer can be suppressed. Herein,an epitaxial layer-provided substrate refers to a substrate having atleast one layer formed by epitaxy (epitaxially grown layer) formed on asurface of a base substrate. Further, in the epitaxial layer-providedsubstrate described above, the number of silicon (Si) atoms per cubiccentimeter at the interface between the base substrate and theepitaxially grown layer may be not more than 1×10¹⁹. In this case, theepitaxially grown layer can be formed to have more excellent quality.The number of silicon atoms per cubic centimeter at the interface ispreferably not more than 1×10¹⁸, and more preferably not more than1×10¹⁷.

In the group III nitride substrate described above, a surface roughnessin Ra may be not more than 1 nm. In the epitaxial layer-providedsubstrate described above, a surface roughness in Ra of a surface of theepitaxially grown layer may be not more than 1 nm. Further, an affectedlayer formed on the surface of the group III nitride substrate describedabove may have a thickness of not more than 50 nm. An affected layerformed on the surface of the base substrate of the epitaxiallayer-provided substrate described above may have a thickness of notmore than 50 nm. Herein, the thickness of the affected layer describedabove can be evaluated by observing the substrate using a transmissionelectron microscope (TEM), defining an area in which crystal latticedistortion occurs as the affected layer, and measuring the thickness ofthe area having distortion (affected layer).

A method of manufacturing a group III nitride substrate according to thepresent invention includes a polishing step of polishing a surface ofthe group III nitride substrate, and a cleaning step of cleaning thesurface of the group III nitride substrate after the polishing step. Anambient gas in contact with the group III nitride substrate iscontrolled during the polishing step and after the cleaning step tomaintain a number of atoms of an acid material per square centimeter ofthe surface of the group III nitride substrate after the cleaning stepto be not more than 2×10¹⁴. In the polishing step, the surface of thegroup III nitride substrate is polished by chemical mechanicalpolishing. A polishing solution used in the chemical mechanicalpolishing contains a surface-active agent and an acid.

With this method, by controlling the ambient gas described above (forexample, by operating an emission mechanism to allow the ambient gascontaining the acid material to be quickly removed from around the groupIII nitride substrate, or by disposing an adsorbing agent for adsorbingthe acid material in a flow path of the ambient gas to allow theconcentration of the acid material contained in the ambient gas to belower than a prescribed value), the possibility that the acid materialadheres from the ambient gas to the surface of the group III nitridesubstrate during the polishing step and after the cleaning step can bereduced. Further, by using the polishing solution as described above inthe polishing step, the possibility that foreign matter (an Sicontaining material) such as abrasive grains (a granular material) madeof SiO₂ or the like in the polishing solution adheres to the surface ofthe group III nitride substrate after the polishing step can be reduced.Therefore, the density of the Si containing material, that is, siliconatoms, on the surface of the group III nitride substrate can be reduced.

In the method of manufacturing a group III nitride substrate describedabove, the polishing solution may further contain an oxidizing agent. Inthis case, a polishing rate in the polishing step can be improved.Therefore, efficiency of manufacturing the group III nitride substratecan be improved.

In the method of manufacturing a group III nitride substrate describedabove, the acid contained in the polishing solution is not particularlylimited, and an inorganic acid such as hydrochloric acid, hydrofluoricacid, bromic acid, iodic acid, nitric acid, sulfuric acid, phosphoricacid, carbonic acid, or the like, as well as an organic acid such asformic acid, acetic acid, citric acid, malic acid, tartaric acid,succinic acid, phthalic acid, fumaric acid, oxalic acid, or the like canbe used, for example. In the method of manufacturing a group III nitridesubstrate described above, the organic acid may be a carboxylic acidhaving a valence of not less than 2. In this case, a polishing rate inthe polishing step can be improved, and the possibility that foreignmatter adheres to the surface of the substrate due to the acid containedin the polishing solution can be reduced. Herein, the organic acidrefers to an organic compound exhibiting acidity. The surface-activeagent contained in the polishing solution is not particularly limited,and any of cationic, anionic, and nonionic surface-active agents may beused.

The method of manufacturing a group III nitride substrate describedabove may further include, after the polishing step and before thecleaning step, a step of polishing the surface of the group III nitridesubstrate using an acid solution or an alkaline solution. In the step ofpolishing, both a step of polishing the surface of the group III nitridesubstrate using an acid solution and a step of polishing the surface ofthe group III nitride substrate using an alkaline solution may beperformed in order, or a step of polishing the surface of the group IIInitride substrate using an acid solution and/or a step of polishing thesurface of the group III nitride substrate using an alkaline solutionmay be repeated a plurality of times. The alkaline solution is notparticularly limited, and a base such as KOH, NaOH, NH₄OH, amine, or thelike can be used. In this case, since foreign matter can be removed fromthe surface of the group III nitride substrate prior to the cleaningstep by the polishing, the probability of occurrence of a problem thatforeign matter (for example, an Si-containing material) remains on thesubstrate surface after the cleaning step can be reduced.

The surface of the substrate can be removed and finished by dry etchinginstead of chemical mechanical polishing. Dry etching refers to any ofthe methods of removing a surface of a group III nitride substrate as asolid by utilizing a chemical or physical reaction at an interfacebetween a vapor phase and a solid phase caused by gas, plasma, ion,light, or the like, without using a liquid.

A chlorine-based gas is often used to dry etch a group III nitridesubstrate, and chlorine as an acid material may be left and present onthe substrate surface. Examples of the chlorine-based gas include Cl₂,BCl₃, SiCl₄, and the like. As the gas used for dry etching, a mixed gascontaining any of these chlorine-based gases and an inert gas such as Aror N₂ can also be employed. The acid material on the substrate surfacecan be reduced by adjusting conditions such as the dilution, thepressure, the flow rate, and the like of the inert gas. Further, tosmooth the surface of the group III nitride substrate by dry etching, itis effective that Si is present in plasma. Si can be added to plasmausing gas such as SiCl₄, or Si can be present in plasma by disposing anSi compound in the vicinity of the substrate and etching the Si compoundsimultaneously with the substrate. There may be a case where, since Siis present in an etching atmosphere, Si remains on the substrate surfacesubjected to dry etching. In this case, silicon on the substrate surfacecan be reduced by controlling the concentration of Si in plasma.

Further, in a method of manufacturing a group III nitride substrateaccording to the present invention, a surface of the group III nitridesubstrate is dry etched within an atmosphere containing Si using achlorine-based gas, and thereby a number of atoms of an acid materialper square centimeter of the surface is not more than 2×10¹⁴, and anumber of silicon atoms per square centimeter of the surface is not morethan 3×10¹³. Herein, the chlorine-based gas refers to a gas containingchlorine in the composition of constituents thereof, and may be, forexample, a chlorine gas or a gas containing chlorine in the compositionthereof, or a mixed gas containing at least one type of these gases.

A method of manufacturing an epitaxial layer-provided substrateaccording to the present invention includes a substrate preparation stepof performing the method of manufacturing a group III nitride substratedescribed above, and a step of forming an epitaxially grown layer on asurface of the group III nitride substrate obtained by the substratepreparation step. With this method, an epitaxially grown layer of goodquality can be formed on the surface of the group III nitride substrate.

A method of manufacturing an epitaxial layer-provided substrateaccording to the present invention includes a substrate preparation stepof preparing the group III nitride substrate described above, and a stepof forming an epitaxially grown layer on a surface of the group IIInitride substrate prepared by the substrate preparation step. With thismethod, an epitaxially grown layer of good quality can be formed on thesurface of the group III nitride substrate.

A method of manufacturing a semiconductor device according to thepresent invention includes an epitaxial layer-provided substratepreparation step of performing the method of manufacturing an epitaxiallayer-provided substrate described above, and a step of forming thesemiconductor device by performing an electrode formation step and aprocessing step on the epitaxial layer-provided substrate obtained bythe epitaxial layer-provided substrate preparation step. With thismethod, a semiconductor device can be formed using an epitaxiallayer-provided substrate having an epitaxially grown layer of excellentquality, and thus the probability of occurrence of failure in thesemiconductor device due to poor quality of the epitaxially grown layercan be reduced. Therefore, a reduction in the yield of the semiconductordevice can be suppressed.

It is to be noted that, if the group III nitride substrate of thepresent invention described above is a GaN substrate, a plane other thana Ga plane of a C plane in the substrate has a low chemical resistance,when compared with the Ga plane of the C plane. Thus, if the planeorientation of the surface of the substrate is set as described above,it is effective to improve a rate in chemical mechanical polishing (CMP)and reactive ion etching (RIE). In addition, a difference in chemicaland mechanical resistance between a front surface and a rear surface ofthe substrate is also reduced. Thus, if the front surface of thesubstrate is the normal C plane, there arises a large difference in thedegree with which a processing distortion layer remains between thefront surface and the rear surface of the substrate, and thereby a largewarpage occurs in the substrate. Occurrence of such a warpage makes itdifficult to perform a process such as polishing on the substrate. Incontrast, if the front surface of the substrate is a plane other thanthe C plane as described above, the difference in chemical andmechanical resistance between the front surface and the rear surface ofthe substrate is small, and thereby the warpage that occurs in thesubstrate is small. Therefore, the process such as polishing can beeasily performed on the substrate.

Further, the GaN substrate has polarity in a [0001] direction (c-axisdirection) in the wurtzite structure. Here, the c-axis is referred to asa polar axis. Further, a plane perpendicular to the polar axis (c-axis)is referred to as a polar plane. That is, the polar plane can be definedas a plane (crystal plane) that is polarized in a directionperpendicular to that plane. Further, a plane parallel to the polar axisis referred to as a non-polar plane. Further, a plane obliquely crossingwith respect to the polar axis is referred to as a semi-polar plane. Ina semiconductor device such as an LED and a laser diode (LD)manufactured using a GaN substrate having a front surface (main surface)which is a non-polar plane (for example, an M plane, an A plane, or thelike), high light emission efficiency is obtained, and, even when thecurrent density of a current to be applied is increased, blue shift ofemission wavelength (that is, shift of emission wavelength to a shorterwavelength side) is suppressed.

In addition, if it is desired in manufacturing a semiconductor device togrow an epitaxial layer with good crystal quality on the main surface ofthe GaN substrate, to form an InGaN layer as the epitaxial layer, and toincrease an uptake quantity of In in the InGaN layer, the main surfaceof the GaN substrate is preferably a semi-polar plane. For example, themain surface of the GaN substrate forming the epitaxial layer describedabove is preferably a (20-21) plane, an S plane, an R plane, a (11-21)plane, a (11-22) plane, a (11-24) plane, or the like. It is to be notedthat, from the viewpoint of the crystal quality and the uptake amount ofIn of the epitaxial layer to be formed, the main surface of the GaNsubstrate may have an off angle of not more than 15° with respect toeach plane orientation described above. Further, if a laser diode isproduced using the substrate, an end surface of a resonator of the laserdiode is preferably an M plane or a C plane having cleavage. Therefore,it is preferable to use a GaN substrate having a main planeperpendicular to an M plane (for example, an A plane, a (11-21) plane, a(11-22) plane, or the like), or having a main plane perpendicular to a Cplane (for example, an M plane, an A plane, or the like). It is to benoted that, from the viewpoint of cleavage, a plane having an off angleof not more than 5° with respect to each plane orientation describedabove can be used as a main surface.

Effects of the Invention

As described above, according to the present invention, an epitaxiallayer-provided substrate having an epitaxially grown layer of excellentquality formed on a surface of a group III nitride substrate can beobtained. Therefore, the probability of occurrence of failure in asemiconductor device can be reduced by forming the semiconductor deviceusing the epitaxial layer-provided substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a GaN substrate as anexample of a group III nitride substrate according to the presentinvention.

FIG. 2 is a flowchart for illustrating a method of manufacturing asemiconductor device using the GaN substrate shown in FIG. 1.

FIG. 3 is a flowchart for illustrating details of a processing stepshown in FIG. 2.

FIG. 4 is a schematic perspective view showing an epitaxiallayer-provided substrate using the GaN substrate shown in FIG. 1.

DESCRIPTION OF THE REFERENCE SIGNS

1: substrate, 3: surface, 5: epitaxially grown layer, 10: epitaxiallayer-provided substrate.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments and examples of the present invention will bedescribed with reference to the drawings, in which identical orcorresponding parts will be designated by the same reference numerals,and the description thereof will not be repeated.

FIG. 1 is a schematic perspective view showing a GaN substrate as anexample of a group III nitride substrate according to the presentinvention. FIG. 2 is a flowchart for illustrating a method ofmanufacturing a semiconductor device using the GaN substrate shown inFIG. 1. FIG. 3 is a flowchart for illustrating details of a processingstep shown in FIG. 2. FIG. 4 is a schematic perspective view showing anepitaxial layer-provided substrate using the GaN substrate shown inFIG. 1. Referring to FIGS. 1 to 4, embodiments of a GaN substrate, anepitaxial layer-provided substrate, and a method of manufacturing asemiconductor device according to the present invention will bedescribed.

As shown in FIG. 1, in a GaN substrate 1 according to the presentinvention subjected to a treatment step described later, the number ofatoms of an acid material (for example, chlorine atoms) per squarecentimeter of a surface thereof (for example, after polishing andcleaning) is not more than 2×10¹⁴, and the number of silicon atoms persquare centimeter of the surface is not more than 3×10¹³. Further, inGaN substrate 1, a haze level of the surface is not more than 5 ppm.With this constitution, an epitaxially grown layer of good quality canbe formed on a surface of a group III nitride substrate.

In GaN substrate 1 described above, the number of atoms of the acidmaterial per square centimeter of a surface 3 is preferably not morethan 9×10¹³. Further, in GaN substrate 1 described above, the haze levelof surface 3 is preferably not more than 3 ppm. Furthermore, in GaNsubstrate 1 described above, the number of silicon atoms per squarecentimeter of surface 3 is preferably not more than 1×10¹³. Further, asurface roughness in Ra in surface 3 of GaN substrate 1 is preferablynot more than 1 nm. Furthermore, an affected layer formed on surface 3due to processing on surface 3 as described later preferably has athickness of not more than 50 nm.

In this case, the film quality of an epitaxially grown layer 5 (see FIG.4) formed on surface 3 of GaN substrate 1 can be further improved. Forexample, when GaN substrate 1 is used to form a light emitting deviceand the epitaxially grown layer is used to form a light emission layeras described later, light emission intensity of the light emission layercan be further increased.

It is to be noted that the number of atoms of the acid material and thenumber of silicon atoms described above were measured using a TXRF(Total X-ray Reflection Fluorescence) instrument, and the haze level wasmeasured using SURFSCAN 4500 manufactured by Tencor.

Further, a crystal structure of GaN substrate 1 is a wurtzite structure,and its surface 3 is preferably any of a (0001) plane, a (11-20) plane,a (10-12) plane, a (10-10) plane, a (20-21) plane, a (10-11) plane, a(11-21) plane, a (11-22) plane, and a (11-24) plane, or a plane havingan off angle of not more than 15° with respect to each plane orientationdescribed above. The off angle is more preferably not more than 10°, andfurther preferably not more than 5°. By setting the plane orientation ofsurface 3 of GaN substrate 1 as described above, occurrence of a warpagein GaN substrate 1 can be suppressed, and epitaxially grown layer 5excellent in crystallinity can be formed. For example, by setting theplane orientation of surface 3 of GaN substrate 1 as a non-polar planesuch as an M plane (a (10-10) plane and a plane equivalent thereto) andan A plane (a (11-20) plane and a plane equivalent thereto) describedabove, light emission efficiency can be improved and so-called blueshift can be suppressed in a semiconductor device such as a lightemitting device manufactured using GaN substrate 1.

Further, by setting the plane orientation of surface 3 of GaN substrate1 as a semi-polar plane such as a (20-21) plane described above,epitaxially grown layer 5 excellent in crystallinity can be formed onsurface 3. It is to be noted that, considering the crystallinity ofepitaxially grown layer 5 and the like, surface 3 of GaN substrate 1 mayhave an off angle of not more than 15° with respect to the semi-polarplane. Further, if a laser diode is formed using GaN substrate 1, an endsurface of a resonator is set as an M plane or a C plane havingcleavage, and thus it is preferable to use a main plane perpendicular toan M plane (for example, an A plane, a (11-21) plane, a (11-22) plane,or the like), or a main plane perpendicular to a C plane (for example,an M plane, an A plane, or the like), as surface 3. It is to be notedthat, from the viewpoint of cleavage, a plane having an off angle of notmore than 5° with respect to each plane orientation described above canbe used as a main surface.

Next, referring to FIGS. 2 and 3, a method of manufacturing asemiconductor device including a step of manufacturing the GaN substrateshown in FIG. 1 will be described.

As shown in FIG. 2, a preparation step (S100) as a step of preparing theGaN substrate is firstly performed. In the preparation step (S100), theGaN substrate can be prepared using any conventionally known method.

Then, a processing step (S200) performing polishing and the like on theGaN substrate is performed. Referring to FIG. 3, treatment details ofthe processing step (S200) will be described. As shown in FIG. 3, in theprocessing step (S200), a CMP step (S210) as a polishing step is firstlyperformed. In the CMP step (S210), the surface of the GaN substrateprepared in the preparation step (S100) is polished by CMP (chemicalmechanical polishing). As a result, the surface of the GaN substrate ismirror finished.

On this occasion, not only abrasive grains but also a surface-activeagent and an acid are added to a polishing solution used in the CMP step(S210). As the abrasive grains contained in the polishing solution,SiO₂, Al₂O₃, ZrO₂, CeO₂, Fe₂O₃, Cr₂O₃, or the like can be used, forexample. To improve cleaning performance, it is preferable to use ametal element having a high ionization tendency as a metal elementconstituting the abrasive grains. For example, if abrasive grainscontaining a metal element having an ionization tendency higher thanthat of hydrogen (H) is used, the efficiency of removing abrasive grainsand the like in a cleaning step described later is increased. As theacid, hydrochloric acid or the like may be used, and an organic acidsuch as malic acid, citric acid, or the like can also be used.Preferably, a carboxylic acid having a valence of not less than 2 isused as the organic acid. In addition, an oxidizing agent may be furtheradded to the polishing solution. Examples of the oxidizing agent usedpreferably include hypochlorous acid and hypochlorite, chlorinatedisocyanuric acid such as trichloroisocyanuric acid (TCIA), chlorinatedisocyanurate such as sodium dichloroisocyanurate, permanganate such aspotassium permanganate, dichromate such as potassium dichromate, bromatesuch as potassium bromate, thiosulfate such as sodium thiosulfate,persulfate such as ammonium persulfate and potassium persulfate, nitricacid, aqueous hydrogen peroxide, ozone, and the like.

Next, a polishing step (S220) is performed. In the polishing step, anacid or alkaline polishing solution is used. As the acid polishingsolution, for example, hydrochloric acid, nitric acid, phosphoric acid,citric acid, malic acid, or the like can be used. As the alkalinepolishing solution, for example, potassium hydroxide, sodium hydroxide,sodium carbonate, or the like can be used.

Then, a cleaning step (S230) is performed. In the cleaning step (S230),any cleaning method can be utilized. For example, pure water cleaningusing pure water may be performed as the cleaning step (S230). At leastduring the CMP step (S210), during the polishing step (S220), and in astep after the cleaning step (S230), an ambient gas in contact with theGaN substrate (i.e., an ambient gas within a clean room in which the GaNsubstrate is treated) is emitted from around the GaN substrate to allowthe concentration of an acid material, in particular chlorine atoms, tobe maintained low, and an adsorbing agent adsorbing the acid material isdisposed in a circulation system of the ambient gas. As the adsorbingagent, for example, activated carbon is used. In this manner, theconcentration of an acid material, in particular chlorine atoms, withinthe ambient gas is maintained at not more than a prescribed value (forexample, not more than 0.02 ppm). As a result, the number of atoms ofchlorine as an acid material adhering to the surface of the GaNsubstrate after polishing and cleaning can be reduced. It is to be notedthat, also during the polishing step (S220), an ambient gas in contactwith the GaN substrate may be emitted from around the GaN substrate asdescribed above, and an adsorbing agent adsorbing the acid material maybe disposed in a circulation system of the ambient gas.

By performing the steps as described above, GaN substrate 1 as shown inFIG. 1 having sufficiently small densities of atoms of an acid materialand silicon on the surface thereof can be obtained. It is to be notedthat, in the processing step (S200), the surface of the GaN substratecan be treated by a dry etching step instead of the CMP step. The dryetching step can also be performed in addition to the CMP step.

Next, as shown in FIG. 2, a post-treatment step (S300) is performed onthe GaN substrate mirror finished by the processing step (S200). In thepost-treatment step (S300), for example, a step of forming a prescribedepitaxially grown layer on the surface of the GaN substrate (a filmforming step) is performed. As a result of the film forming step, anepitaxial layer-provided substrate 10 having an epitaxially grown layer5 formed on the surface of GaN substrate 1 as shown in FIG. 4 can beobtained. Further, in the post-treatment step (S300), an assembly stepof assembling a device such as a light emitting device is implemented byperforming a step of forming an electrode on a surface of epitaxiallayer-provided substrate 10 (an electrode forming step), a separationstep of separating epitaxial layer-provided substrate 10 into individualdevices, and a step of connecting the formed device to a frame (aprocessing step).

Embodiments of the present invention will be enumerated and described,although they partly overlap with the embodiment described above. Amethod of manufacturing a group III nitride substrate (GaN substrate 1)according to the present invention includes a polishing step (CMP step(S210)) of polishing a surface of GaN substrate 1, and a cleaning step(S230) of cleaning the surface of GaN substrate 1 after the CMP step(S210). An ambient gas in contact with GaN substrate 1 is controlledduring the polishing step (CMP step (S210)) and after the cleaning step(S230) to maintain the number of atoms of an acid material per squarecentimeter of the surface of GaN substrate 1 after the cleaning step(S230) to be not more than 2×10¹⁴. Specifically, an adsorption memberadsorbing the acid material, such as activated carbon, is disposedwithin the ambient gas to maintain the concentration of the acidmaterial within the ambient gas to be not more than a prescribed value.Further, during the CMP step (S210) and after the cleaning step (S230)described above, an emission mechanism may be provided to maintain theconcentration of the acid material within the ambient gas to be not morethan a prescribed value. In the CMP step (S210), the surface of GaNsubstrate 1 is polished by chemical mechanical polishing. A polishingsolution used in the chemical mechanical polishing contains asurface-active agent and an acid.

With this method, the ambient gas described above is controlled suchthat the acid material is removed from the ambient gas, and thus thepossibility that the acid material adheres from the ambient gas to thesurface of GaN substrate 1 during the CMP step and after the cleaningstep can be reduced. Further, by using the polishing solution asdescribed above in the CMP step (S210), the possibility that an Sicontaining material in the polishing solution adheres to the surface ofGaN substrate 1 after the CMP step (S210) can be reduced. Therefore, thedensity of the Si containing material, that is, silicon atoms, on thesurface of GaN substrate 1 can be reduced.

In the CMP step (S210) described above, the polishing solution mayfurther contain an oxidizing agent. In this case, a polishing rate inthe polishing step can be improved.

Further, the acid contained in the polishing solution may be an organicacid. Furthermore, the organic acid may be a carboxylic acid having avalence of not less than 2. In this case, a polishing rate in thepolishing step can be improved, and the possibility that foreign matteradheres to the surface of the substrate due to the acid contained in thepolishing solution can be reduced.

The method of manufacturing a GaN substrate described above may furtherinclude, after the CMP step (S210) and before the cleaning step (S230),a step of polishing the surface of GaN substrate 1 using an acidsolution or an alkaline solution (the polishing step (S220)). In thepolishing step (S220), both a step of polishing the surface of GaNsubstrate 1 using an acid solution and a step of polishing the surfaceof GaN substrate 1 using an alkaline solution may be performed in order,or a step of polishing the surface of GaN substrate 1 using an acidsolution and/or a step of polishing the surface of GaN substrate 1 usingan alkaline solution may be repeated a plurality of times. In this case,since foreign matter can be removed from the surface of GaN substrate 1prior to the cleaning step by the polishing, the probability ofoccurrence of a problem that foreign matter remains on the surface ofGaN substrate 1 after the cleaning step (S230) can be reduced. Further,since the acid material can also be reduced prior to the cleaning stepby the polishing step, the existing amount thereof after the cleaningstep can be reduced.

Further, dry etching can be performed instead of the CMP step. Examplesof the dry etching include RIE (Reactive Ion Etching), ICP (InductivelyCoupled Plasma)-RIE, ECR (Electron Cyclotron Resonance)-RIE, CAIBE(Chemical Assist Ion Beam Etching), RIBE (Reactive Ion Beam Etching),and the like.

A method of manufacturing an epitaxial layer-provided substrateaccording to the present invention includes a substrate preparation step(the processing step (S200) in FIG. 2) of performing the method ofmanufacturing a GaN substrate described above (or preparing GaNsubstrate 1 as the group III nitride substrate described above), and astep of forming an epitaxially grown layer (the film forming stepincluded in the post-treatment step (S300)) on a surface of the groupIII nitride substrate obtained by the processing step (S200). With thismethod, epitaxially grown layer 5 of good quality can be formed onsurface 3 of GaN substrate 1.

A method of manufacturing a semiconductor device according to thepresent invention includes an epitaxial layer-provided substratepreparation step (the processing step (S200) and the film forming step)of performing the method of manufacturing an epitaxial layer-providedsubstrate described above, and a step of forming the semiconductordevice (steps after the film forming step in the post-treatment step(S300)) by performing an electrode formation step and a processing step(included in the post-treatment step (S300)) on epitaxial layer-providedsubstrate 10 obtained by the epitaxial layer-provided substratepreparation step. With this method, the semiconductor device can beformed using epitaxial layer-provided substrate 10 having epitaxiallygrown layer 5 of excellent quality, and thus the probability ofoccurrence of failure in the semiconductor device due to poor quality ofepitaxially grown layer 5 can be reduced.

Further, epitaxial layer-provided substrate 10 according to the presentinvention includes GaN substrate 1 as a base substrate made of a groupIII nitride, and epitaxially grown layer 5 formed on surface 3 of GaNsubstrate 1, as shown in FIG. 4. The number of silicon (Si) atoms percubic centimeter at an interface between GaN substrate 1 and epitaxiallygrown layer 5 is not more than 1×10²⁰. Furthermore, epitaxiallayer-provided substrate 10 according to the present invention includesGaN substrate 1 as the group III nitride substrate according to thepresent invention described above, and an epitaxially grown layer formedon a surface of GaN substrate 1.

In epitaxial layer-provided substrate 10 constructed as described above,epitaxially grown layer 5 is formed with the number of silicon atoms onthe surface of GaN substrate 1 maintained low, and thus epitaxiallygrown layer 5 can be formed to have good quality. Therefore, occurrenceof a problem that, when epitaxial layer-provided substrate 10 describedabove is used to form, for example, a light emitting device, the devicebecomes defective due to poor quality of epitaxially grown layer 5 canbe suppressed.

Further, in the epitaxial layer-provided substrate described above, thenumber of silicon (Si) atoms per cubic centimeter at the interfacebetween GaN substrate 1 and epitaxially grown layer 5 may be not morethan 1×10¹⁹. In this case, epitaxially grown layer 5 can be formed tohave more excellent quality. The number of silicon (Si) atoms per cubiccentimeter at the interface between GaN substrate 1 and epitaxiallygrown layer 5 (the density of Si atoms) can be measured by SIMS(Secondary Ion Mass Spectrometry). For example, measurement can beperformed using a magnetic sector SIMS instrument manufactured by CAMECAas a measuring instrument, and under a measurement condition that Cs⁺ isused as a primary ion.

Example 1

To confirm the effect of the present invention, experiments as describedbelow were conducted.

(Preparation of Samples)

Samples of examples 1 to 13 were prepared as samples of the examples ofthe present invention, and samples of comparative examples 1 to 4 wereprepared as comparative examples. Specifically, GaN substrates to serveas examples 1 to 13 and comparative examples 1 to 4 were prepared. TheGaN substrates were all in the shape of a disk with a diameter of 50 mmand a thickness of 0.5 mm. For these GaN substrates, lapping wasperformed beforehand on a surface thereof, using diamond abrasivegrains. As the abrasive grains used for the lapping, abrasive grainswith an average diameter of 6 μm, 2 μm, and 0.5 μm were preparedrespectively, and the lapping was performed, firstly using the abrasivegrains with a larger diameter, and then using the abrasive grains with asmaller diameter, in a step-by-step manner. After the lapping, polishingwas performed using alumina abrasive grains. As the alumina abrasivegrains, those with an average diameter of 0.5 μm were used. In thismanner, the surfaces of the samples of the GaN substrates werepretreated.

(Polishing of Samples)

Processing as described below was performed on the GaN substratesprepared as described above, within a clean room. It is to be notedthat, to maintain the concentration of an acid material, in particularchlorine atoms, sufficiently low in an ambient gas within a polishingapparatus installed in the clean room, the ambient gas was able to beemitted from the inside of a treatment chamber in which the GaNsubstrates were disposed. The ambient gas was emitted at an emissionwind speed of 0.6 m/s. In the polishing apparatus, the surfaces of theGaN substrates to serve as examples 1 to 8 and 11 to 13 were polished byCMP. As shown in Table 1, polishing solutions used for the polishing forexamples 1 to 8 contained SiO₂ as abrasive grains. Polishing solutionsused for the polishing for examples 11 to 13 contained ZrO₂, Cr₂O₃,Fe₂O₃, respectively, as abrasive grains. The polishing solutionscontained hydrochloric acid, malic acid, or citric acid, as an acid foradjusting pH. With these acids added thereto, the polishing solutionshad pHs of around not less than 2 and not more than 4. Further, 0.05percent by mass of sodium polyacrylate was added as a surface-activeagent to the polishing solutions. Furthermore, as an oxidizing agent,0.1 percent by mass of trichloroisocyanuric acid (TCIA) was added to thepolishing solutions used in examples 2, 5, 6, and 10 to 13, hypochlorousacid was added in examples 1 and 7, and sodium dichloroisocyanurate(Na-DCIA) was added in example 3. In examples 4 and 8, polishingsolutions not containing an oxidizing agent were used. After thepolishing step, pure water cleaning was performed to obtain the GaNsubstrates having a mirror-finished surface. For each of these GaNsubstrates, concentrations of Si and chlorine on the surface, a surfaceroughness and a haze level of the surface, and a thickness of anaffected layer were measured as described later.

For example 9, the GaN substrate as a sample for measuring the Siconcentration on the surface and the like was prepared by processing theGaN substrate by a technique called dry etching (DE). The dry etchingfor the processing was performed using a parallel plate type RIEapparatus. The processing was performed under a condition that Cl₂ gasand BCl₃ gas were used as etching gases, with a flow rate of the Cl₂ gasbeing 25 sccm (sccm: a unit of a flow rate at which one cubic centimeterof gas in a standard state flows per minute; hereinafter the sameapplies) and a flow rate of the BCl₃ gas being 25 sccm, at a pressure of2.66 Pa and at an RF power of 200 W.

For example 10, polishing by CMP as in example 1 was performed, and thenpolishing (cleaning polishing) was performed. In the polishing, asolution containing 0.3 percent by mass of citric acid and 0.1 percentby mass of TCIA was used as a polishing solution. Thereafter, thecleaning step was performed as in examples 1 to 9 to prepare the GaNsubstrate as a sample for measuring the Si concentration on the surfaceand the like.

Also for comparative examples 1 to 4, the surfaces of the GaN substrateswere polished by CMP. However, for comparative example 1, a polishingsolution containing abrasive grains made of SiO₂ and hydrochloric acidfor adjusting pH was used. For comparative example 2, a polishingsolution containing abrasive grains made of SiO₂, malic acid foradjusting pH, a surface-active agent (sodium polyacrylate), and anoxidizing agent (TCIA) was used. For comparative example 3, a polishingsolution containing diamond abrasive grains, malic acid for adjustingpH, a surface-active agent (sodium polyacrylate), and an oxidizing agent(TCIA) was used. For comparative example 4, a polishing solutioncontaining abrasive grains made of SiC, malic acid for adjusting pH, asurface-active agent (sodium polyacrylate), and an oxidizing agent(TCIA) was used. Contents of the surface-active agent and the oxidizingagent were 0.3 percent by mass and 0.1 percent by mass, respectively.

Subsequently, for comparative examples 1 to 4, the GaN substrates assamples for measuring the Si concentrations on the surface and the likewere prepared by performing pure water cleaning after the polishing stepas in examples 1 to 8 and 11 to 13.

It is to be noted that, from when the processing step described abovewas performed to when measurement described below was performed, theambient gas within the apparatus was emitted in examples 1 to 13 andcomparative examples 1, 3, and 4, whereas the ambient gas was notemitted in comparative example 2.

(Measurement of Substrate Surface)

For each of the samples (GaN substrates) of examples 1 to 13 andcomparative examples 1 to 4 prepared as described above, substrateproperties were measured. Specifically, the concentrations of silicon(Si) and chlorine (Cl) on the mirror-finished surface, the surfaceroughness and the haze level of the surface, and the thickness of anaffected layer were measured. Table 1 shows results thereof.

TABLE 1 Examples 1 2 3 4 5 6 7 8 9 10 11 12 Manufacturing Method CMP CMPCMP CMP CMP CMP CMP CMP DE Cleaning CMP CMP Polishing Polishing AbrasiveGrains SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ — — ZrO₂ Cr₂O₃ SolutionpH Adjustment HCl HCl HCl HCl Malic Citric Citric Malic — Citric MalicMalic Acid Acid Acid Acid Acid Acid Acid Oxidizing Agent HClO TCIA Na- —TCIA TCIA HClO — — TCIA TCIA TCIA DCIA Surface-Active ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ —— ◯ ◯ Agent Atmosphere emitted emitted emitted emitted emitted emittedemitted emitted emitted emitted emitted emitted Substrate SiConcentration 2.7 2.5 2.3 3.0 0.5 0.6 0.7 0.8 0.1 0.2 ND ND Properties(×10¹³/cm²) Cl Concentration 18 20 17 15 8 7 9 ND 12 7 8 7 (×10¹³/cm²)Surface Roughness 0.45 0.42 0.41 0.40 0.30 0.35 0.37 0.41 0.83 0.35 0.680.95 Ra (nm) Haze Level (ppm) 2.3 2.1 2.0 2.2 1.4 1.7 1.8 2.5 5.0 1.73.2 5.0 Affected Layer 0 0 0 0 0 0 0 0 0 0 30 50 Processing RemovalSpeed 1.0 1.2 1.1 0.6 1.5 1.3 1.2 0.9 5.2 — 2.5 3.2 Property (μm/hr) EpiSurface Roughness 0.30 0.31 0.31 0.28 0.22 0.25 0.26 0.33 0.51 0.25 0.420.52 Property Ra (nm) Device Light Emission 2.2 2.3 2.3 2.5 3.2 2.9 2.82.0 1 3.3 1.1 0.91 Property Intensity (Relative Value) ExamplesComparative Examples 13 1 2 3 4 Manufacturing Method CMP CMP CMP CMP CMPPolishing Abrasive Grains Fe₂O₃ SiO₂ SiO₂ diamond SiC Solution pHAdjustment Malic HCl Malic Malic Malic Acid Acid Acid Acid OxidizingAgent TCIA — TCIA TCIA TCIA Surface-Active ◯ — ◯ ◯ ◯ Agent Atmosphereemitted emitted not emitted emitted emitted Substrate Si ConcentrationND 7.0 0.8 ND 0.7 Properties (×10¹³/cm²) Cl Concentration 7 12 43 8 8(×10¹³/cm²) Surface Roughness 0.56 0.51 2.3 3.1 2.6 Ra (nm) Haze Level(ppm) 2.7 2.8 12 16 8.2 Affected Layer 0 0 0 300 150 Processing RemovalSpeed 1.8 1.0 1.1 4.8 4.0 Property (μm/hr) Epi Surface Roughness 0.352.5 2.6 >100 >100 Property Ra (nm) Device Light Emission 1.8 — — — —Property Intensity (Relative Value) TCIA: trichloroisocyanuric acidNa-DCIA: sodium dichloroisocyanurate HCl: hydrochloric acid HClO:hypochlorous acid

As to the Si concentration and the Cl concentration, the number of atomsper square centimeter was inspected at a central portion of thesubstrate surface using a Total X-ray Reflection Fluorescence (TXRF)instrument, and Table 1 shows values thereof. The surface roughness wasmeasured at five points on the substrate surface, and Table 1 shows anaverage value thereof. The haze level was measured using SURFSCAN 4500manufactured by Tencor. The thickness of an affected layer was evaluatedby observing distortion of a crystal lattice of the GaN substrate usinga TEM.

As can be seen from Table 1, in examples 1 to 8 in which the polishingsolutions used for CMP contained an acid such as hydrochloric acid orcitric acid and a surface-active agent, the Si concentrations weresignificantly lower than that of comparative example 1 in which thepolishing solution did not contain a surface-active agent. It can alsobe seen that, of examples 1 to 8, the Si concentrations wereparticularly reduced in examples 5 to 8 in which malic acid or citricacid was used as the acid in the polishing solutions. In examples 11 and13 and comparative example 3 in which abrasive grains other than SiO₂and SiC (abrasive grains not containing Si as an element) were used asthe abrasive grains in the polishing solutions used for CMP, Si was notdetected from the substrate surfaces.

Further, it can be seen that all the samples obtained with theatmosphere being emitted during treatment exhibited low values of the Clconcentration, the surface roughness, and the haze level, whereas thesample of comparative example 2 in which the atmosphere was not emittedhad relatively high values of the Cl concentration, the surfaceroughness, and the haze level. In addition, the thicknesses of affectedlayers in examples 1 to 13 were all smaller than those in comparativeexamples 3 and 4. In particular, in examples 1 to 10 and 13 in whichSiO₂ or Fe₂O₃ was used as the abrasive grains, no affected layer wasdetected. Although an affected layer was detected in examples 11 and 12,the thicknesses thereof were sufficiently smaller than those incomparative examples 3 and 4.

It can also be seen that, in examples 1 to 3, 5 to 7, and 11 to 13 inwhich the polishing solutions contained an oxidizing agent, removalspeeds in the polishing step were greater than those in examples 4 and 8in which the polishing solutions did not contain an oxidizing agent.

(Fabrication of Light Emitting Device)

For each of the samples (GaN substrates) of examples 1 to 13 andcomparative examples 1 to 4 processed as described above, a plurality ofepitaxially grown layers were formed on the surface thereof, and thenelectrode formation, separation into individual chips, mounting of thechip onto a lead frame, and the like were performed to fabricate a lightemitting device (LED). The epitaxially grown layers formed on thesurface of the GaN substrate specifically included a 1 μm-thick n-typeGaN layer (dopant: Si) and a 150 nm-thick n-type Al_(0.1)Ga_(0.9)N layer(dopant: Si) as n-type semiconductor layers, a light emission layer, anda 20 nm-thick p-type Al_(0.2)Ga_(0.8)N layer (dopant: Mg) and a 150nm-thick p-type GaN layer (dopant: Mg) as p-type semiconductor layers.The light emission layer had a multiple quantum well structure in whichfour barrier layers each formed of a 10 nm-thick GaN layer and threewell layers each formed of a 3 nm-thick Ga_(0.85)In_(0.15)N layer werestacked alternately.

As a first electrode, a layered structure including a 200 nm-thick Tilayer, a 1000 nm-thick Al layer, a 200 nm-thick Ti layer, and a 2000nm-thick Au layer was formed on a rear surface of the substrate, andheated in a nitrogen atmosphere to form an n-side electrode with adiameter of 100 μm. As a second electrode, a layered structure includinga 4 nm-thick Ni layer and a 4 nm-thick Au layer was formed on the p-typeGaN layer described above, and heated in an inert gas atmosphere to forma p-side electrode. The layered body described above (i.e., the GaNsubstrate having the epitaxially grown layers, the n-side electrode, andthe p-side electrode as described above formed thereon) was separatedinto chips of 400 μm per side, and thereafter the p-side electrode wasbonded to a conductor with a solder layer made of AuSn. Further, then-side electrode and the conductor were bonded with a wire, and thus asemiconductor device having a structure as a light emitting device wasobtained.

(Measurement for Epitaxially Grown Layers)

Surface roughnesses of the epitaxially grown layers formed on thesurfaces of the GaN substrates of examples 1 to 13 and comparativeexamples 1 to 4 prepared as described above were measured by the sametechnique as that used for measuring the surface roughnesses of the GaNsubstrates described above. Table 1 also shows results thereof. As canbe seen from Table 1, the surface roughnesses of the epitaxially grownlayers in examples 1 to 13 were smaller than those in comparativeexamples 1 to 4.

The Si concentration at an interface between the substrate and theepitaxial layer was measured by SIMS. The Si concentrations in examples1, 5, 10, and 13, and comparative example 1 were 1×10²⁰/cm³, 1×10¹⁹/cm³,1×10¹⁸/cm³, 1×10¹⁷/cm³, and 5×10²⁰/cm³, respectively. The siliconconcentrations at the interfaces in examples 1, 5, 10, and 13 weresmaller than that in comparative example 1.

(Measurement of Light Emission Intensity)

Light emission intensities of the light emitting devices of examples 1to 13 and comparative examples 1 to 4 prepared as described above weremeasured. Table 1 also shows results thereof. As can be seen from Table1, light emission did not occur in the light emitting devices ofcomparative examples 1 to 4, whereas light emission in the lightemission layer of the epitaxially grown layers was confirmed in thelight emitting devices of examples 1 to 13. To measure a light emissionintensity, a light emitting device as each sample was mounted within anintegrating sphere, a prescribed current (20 mA) was applied to thelight emitting device, emitted light was collected at a detector, and alight output value output from the detector was measured.

Although the embodiments and the examples of the present invention havebeen described, the embodiments and the examples of the presentinvention disclosed above are by way of illustration only, and the scopeof the present invention is not limited to these embodiments of thepresent invention. The scope of the present invention is defined by thescope of the claims, and is intended to include any modifications withinthe scope and meaning equivalent to the scope of the claims.

INDUSTRIAL APPLICABILITY

The present invention is particularly advantageously applicable to agroup III nitride substrate used for a light emitting device, a powerdevice, and the like, an epitaxial layer-provided substrate using thegroup III nitride substrate, and methods of manufacturing the same.

1. A GaN substrate, having a surface in which a number of chlorine atomsper square centimeter of said surface is not more than 2×10¹⁴, and anumber of silicon atoms per square centimeter of said surface is notmore than 3×10¹³, wherein a plane orientation of said surface is any ofa (0001) plane, a (11-20) plane, a (10-12) plane, a (10-10) plane, a(20-21) plane, a (10-11) plane, a (11-21) plane, a (11-22) plane, and a(11-24) plane of a wurtzite structure.
 2. The GaN substrate according toclaim 1, wherein a surface roughness in Ra is not more than 1 nm.
 3. TheGaN substrate according to claim 1, wherein an affected layer formed onsaid surface has a thickness of not more than 50 nm.
 4. An epitaxiallayer-provided substrate, comprising: the GaN substrate according toclaim 1; and an epitaxially grown layer formed on a surface of said GaNsubstrate.
 5. A method of manufacturing an epitaxial layer-providedsubstrate, comprising: a substrate preparation step of preparing the GaNsubstrate according to claim 1; and a step of forming an epitaxiallygrown layer on a surface of the GaN substrate prepared by said substratepreparation step.
 6. A method of manufacturing a semiconductor device,comprising: an epitaxial layer-provided substrate preparation step ofperforming the method of manufacturing an epitaxial layer-providedsubstrate according to claim 5; and a step of forming the semiconductordevice by performing an electrode formation step and a processing stepon the epitaxial layer-provided substrate obtained by said epitaxiallayer-provided substrate preparation step.